The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The use of sound attenuation panels e.g. in aircraft engine nacelles and of nacelle parts equipped with said panels to reduce noise emissions from turbojet engines is known in the state of the art.
These sound attenuation panels generally have a sandwich structure comprising a structuring skin, an alveolar structure of honeycomb type and a resistive layer generally formed by a perforated acoustic skin.
In some cases, the sound attenuation panels must be designed for installation in a hot zone of the nacelle of the aircraft turbojet engine, and in particular in the downstream part of this nacelle via which exhaust gases are expelled whose temperature is typically higher than 600° C.
The use of sound attenuation panels in this exhaust area allows a substantial reduction in noise emissions which lie in the high frequency range.
For these particular high temperature applications, use is generally made of sound attenuation panels whose structuring skin is formed by a metal sheet, the honeycomb structure is metallic and the resistive layer is a perforated metal sheet.
The metallic honeycomb structure is then joined by brazing (i.e. assembly of two materials using a filler metal having a melt temperature lower than that of the base metal) onto the structuring metallic sheet and the perforated metal sheet.
The use of metal alloys for all the elements forming this sandwich structure and the use of brazing for the joining thereof are particularly high-cost.
Yet such parts are often manufactured from relatively expensive metals or alloys, developed to withstand high-temperature environments whilst preserving necessary properties of strength.
The manufacturing thereof is therefore relatively costly.
Therefore, when one of these panels is damaged either during its assembly or on account of service conditions through thermal fatigue, corrosion, erosion or even impacting with other objects, it is desirable to repair this panel to avoid the expense of a new part.
Another possible deterioration of said panel which requires repair is deterioration of the junction interfaces between the structuring skin, the resistive layer and the honeycomb structure affecting the structural qualities of the panel.
However, assembly or repair operations of such deteriorations by welding or brazing are complex insofar as one of the skins of the sound panel has small-size orifices and the other is solid.
Repair methods are therefore known in which all or part of the skin of a sound panel and/or of the honeycomb structure are replaced. Such methods are costly.
In addition, associated assembly or repair operations are not easy insofar as there is a risk that the acoustic and structural qualities of the panel may be affected by these operations, such as deteriorated mechanical strength of the sandwich panel, even loss of acoustic absorption of the panel.
Also, assembly and repair operations such as welding or brazing have an effect on the metallurgical properties of the treated panel affecting the surface properties thereof.
Defects such as oxidization or cracking may therefore result from repair operations.
When located within the panels, these defects are difficult to remove.